Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

Energy Calibration and Stability ofthe ANKA Storage Ring

A.-S. Müller, I. Birkel, E. Huttel, F. PérezV, M. PontV, R. Rossmanith

Institut für Synchrotronstrahlung – ISS

Forschungszentrum Karlsruhe

V now at ALBA Synchrotron Light Source, Spain

10/12/2004 Energy Calibration of ANKA IWBS2004 – page 1/21

Overview

Brief introduction to ANKA

Why energy stability is an issue at ANKA

How to calibrate the beam energy in a very precise(but simple) wayÜ resonant depolarisationÜ makeshift polarimeter

Summary

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 2/21

Research Centre Karlsruhe

Research & development in various fields:

environmental analysis

medicine/bio technology

material science

microsystem technology

(astro) particle physics

IT science

nano technology

...

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 3/21

ÅNgströmquelle KArlsruheTradition in the production of electromagnetic radiation in KA

1887

First observation of electromagneticwaves in Karlsruhe by Heinrich Hertz

(“Hertz Dipole”)

1996

Ground-breaking ceremony for ANKAFirst beam in 2000Regular user operation since 2001/2002

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 4/21

The ANKA FacilityElectron storage ring witha beam energy of 2.5 GeV

hosts 12 beamlinesÜ running: 6 + 3Ü commissioning: 3Ü planned: 1

Mostly bending magnetbeam linesÜ free space for 5 IDsÜ two installed

Development of SC IDsÜ planar SCU to come

in the near futureÜ first prototype of

helical SCU10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 5/21

The ANKA Storage Ring

4 C = 110.4 m4 0.5 ≤E0 ≤2.5 GeV4 εx = 80 40 nm·rad4 coupling ≈ 1%

7

Beam position reproducibility:

8 6 weeks RMS: 15 µm8 6 weeks RMS without ramp drift: 8 µm8 1 h RMS: < 2 µm

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 6/21

A Typical Day in ANKA’s Life

A typical day at ANKA sees two injections of ≈ 200 mA:re-fills in the morning and late afternoon

Regular user operation at 2.5 GeV

Special operation mode: beam at 1.3 GeV (e.g. for lithography)

This means:Ü large current changesÜ cycling of bends and

quadrupolesÜ ramp (Bdipole range

from 0.3 to 1.5 T)

Compensate thermally in-duced drifts in the bendingfield (E0)

Cur

rent

[mA

], 10

*Ene

rgy

[GeV

]

Life

time

[h]

Days since January 1, 2004

Lifetime

Current

Energy

0

10

20

0

100

200

54.5 55

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 7/21

Field Drift Correction

30 beam position monitors

28 horizontal correctors

16 vertical correctors

SVD based orbit correctionby cosylab

choice between measured ormodel response matrix

RF frequency as a freeparameter in the correction

∆p

p= −

1

αc

(fRF − fcRF)

fRF

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 8/21

Low αc Optics

Since spring 2004 new operation mode with reduced αc for shortbunchesÜ production of CSER in the FIR rangeÜ intensity enhancement of up to 5 orders of magnitude

small changes in correctorstrengths lead to visible energychangesÜ orbit correction with RF

frequency as free parameternecessary for reproducibleconditions

Y.-L. Mathis et al.

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 9/21

External InfluenceRF frequency adjustment keeps path length constant

RF

RF∝

∝ −

daily drifts caused byinjection and rampingscheme

significant seasonaldependence

how well does this trulyreproduce the nominalbeam energy?

10/12/2004 Energy Calibration of ANKA – Introduction IWBS2004 – page 10/21

Energy Calibration

Why do we need to know the beam energy?Ü as a cross-check for the energy correction by frequency

adjustmentÜ for ID characterisation:

εγ ∝ E2 þ 1% ∆E/E Ü 2% ∆εγ/εγ

Ü for further development of optics, an excellent knowledge andunderstanding of the present optics is needed: energy errors aregradient errors!

Measure E0 with highest possible precision: Resonant Depolarisation

10/12/2004 Energy Calibration of ANKA – The Principle IWBS2004 – page 11/21

Transverse Polarisation

Polarisation build-up by emission of synchrotron radiation:

Ü asymmetry in spin flip probability leads to transverse polarisationÜ max. polarisation is given by size of asymmetry term:

8/5√

3 ≈ 92.4%

Polarisation level increases exponentially with build up time

τp =8

5√

3

m60 c10 ρ3

h rc E50

Ü for ANKA at 2.5 GeV: τp ≈ 10 minutes

10/12/2004 Energy Calibration of ANKA – The Principle IWBS2004 – page 12/21

Spin Motion

The motion of the spin vector ~s of a relativistic electron in thepresence of electric and magnetic fields ~E and ~B is described by theThomas-BMT (Bargmann, Michel, Telegdi) equation:

d~s

dt= ~ΩBMT × ~s

The spin precession frequency ~ΩBMT can be written as

~ΩBMT = −e

γm0

[

(1 + aγ) ~B⊥ + (1 + a) ~B‖ −

(

aγ +γ

1 + γ

)

~β ×~E

c

]

a = (ge − 2)/2 = 0.001159652193(10)

The average over all particles of the number of spin oscillations perrevolution is defined as the spin tune

ν = fspin/frev =(ge − 2)/2

m0c2E0

10/12/2004 Energy Calibration of ANKA – The Principle IWBS2004 – page 13/21

Resonant Depolarisation

Horizontal magn. field Bx modulated with fB is applied to the beam

For a certain phase relation between the kicks of the depolariser andthe spin tune the small spin rotations add up coherently from turn toturn and the polarisation is destroyed

Ü resonance condition for spin rotations

fdep = (k ± [ν]) · frev

To determine the spin tune, the frequency of the depolariser field isslowly varied with time over a given frequency range

Ü precision: ∆E/E ≈ 10−5

10/12/2004 Energy Calibration of ANKA – The Principle IWBS2004 – page 14/21

Polarisation and Loss Rate

Touschek cross-section depends on electron beam polarisationÜ use particle loss rate as a measure for polarisation level

Pioneering work byÜ P. Kuske et al., “High Precision Determination of the Energy at

BESSY II”, EPAC 2000Ü C. Steier et al., “Energy Calibration of the Electron Beam of the

ALS Using Resonant Depolarisation”, EPAC 2000Ü S.C. Leeman et al., “Precise Beam

Energy Calibration at the SLSStorage Ring”, EPAC 2002

Set up a beam loss monitor in aTouschek sensitive region...

(test of detector sensitivity) Ü

loss

rate

/ kH

z

time / s

0.5

0.75

1

1.25

1.5

0 50 100 150

Q2 up

Q2 up

Q2 up

Q2 down

Q2 down

Q2 down

10/12/2004 Energy Calibration of ANKA – The Principle IWBS2004 – page 15/21

Polarisation Detection

First attempts with scintillatorswrapped in lead sheets to sup-press the contribution of syn-chrotron radiation to the countrate

Final setup: Pb-Glass block withphoto multiplier

Photo multiplier pulses areconverted to NIM signals andcounted using a custom madeinterface to a Linux PC

10/12/2004 Energy Calibration of ANKA – Measurements and Results IWBS2004 – page 16/21

Some RDP Results∆E

/ E

∆fRF / fRF0

-0.01

-0.005

0

-0.2 0 0.2 0.4 0.6 0.8x 10

-4

Fit to loss rate scans using

r = a −∂rI

∂tt +

∆r

1 + exp

− t−td

σd

Measure αc using RDP scans fordifferent fRF:

∆fRF

fRF= αc1 δ + αc2 δ2

Expectation for linear term:7.2 · 10−3

αc1 = (7.39 ± 0.01) · 10−3

Quadratic term:αc2 = (4.1 ± 0.2) · 10−2

Ü highly significant but small

rela

tive

chan

ge in

loss

rat

e

depolariser frequency [MHz]

-0.05

0

0.05

1.68 1.69 1.7

10/12/2004 Energy Calibration of ANKA – Measurements and Results IWBS2004 – page 17/21

Bunch Lengthening & RDPre

lativ

e ch

ange

in lo

ss r

ate

depolariser frequency [MHz]

depolarisation on Ebeam

depolarisation on Qs side band

-0.1

-0.05

0

0.05

0.1

1.64 1.65 1.66 1.67 1.68 1.69 1.7

inco

here

nt Q

s

coherent Qs

22

24

26

28

30

21 22 23 24 25 26 27 28 29 30

Depolarisation can also occur onsynchrotron side bands

Due to the single particle nature of thedepolarisation process, this happensat fdep/frev = [ν] ± Qinc

s

RMS bunch length: σs ∝ 1/Qincs

The coh./inc ratio is a measure forbunch lengthening with current

Qcohs

Qincs

= 1 − λIbunch

Average coherent/incoherent ratio:(1.02 ± 0.03)Ü no significant lengthening

10/12/2004 Energy Calibration of ANKA – Measurements and Results IWBS2004 – page 18/21

Energy Reproducibility

Fill-to-fill variations of the order of 10−4

Reproducibility within single fill ≈ 10−5

Ebe

am [G

eV]

fill number

2.4775

2.478

2.4785

0 1 2 3 4

Energy drift compensation by RF frequency adjustment seems to workreasonably well

10/12/2004 Energy Calibration of ANKA – Measurements and Results IWBS2004 – page 19/21

Summary

The beam energy is an important parameterfor accelerator and insertion devices

Very precise measurement possible withresonant depolarisation

Detection of polarisation change withTouschek-loss-polarimeter

Energy stability acceptable:

(10

)

4

4

4

4

10/12/2004 Energy Calibration of ANKA – Summary IWBS2004 – page 20/21